Technical Field
The present invention relates to a thermoplastic elastomer composition.
Background Art
Air bag devices for vehicles are installed in steering wheels, in instrument panels in front of passenger seats, under knees of driver seats and passenger seats, in side pillars, etc. The air bag covers of air bag devices are required to have a stiffness suited for each application, such as for a driver seat and a passenger seat, a high tensile strength or tear strength so as not to allow the air bag covers to rupture at a part other than a tear line (namely, a thin-wall part formed so as to allow an air bag cover to rupture upon expansion of the air bag), and a good low-temperature impact resistance so as to withstand use in cold climates.
As such an air bag cover, there has been proposed an injection molded article made of a polyolefin-based thermoplastic elastomer composition comprising a propylene resin and an ethylene-α-olefin copolymer elastomer. For example, US 2012/0259057 A1 discloses an air bag cover made of an elastomer resin composition comprising a propylene polymeric material produced through multistage polymerization, an ethylene-α-olefin-nonconjugated diene copolymer elastomer, and a mineral oil-based softening agent. JP-A-2013-35888 discloses an air bag cover made of an elastomer resin composition comprising a propylene polymeric material produced through multistage polymerization, an ethylene-α-olefin copolymer, and a propylene-ethylene copolymer.
In recent years, air bag covers installed in visible sites such as steering wheels are under investigation for eliminating painting and are requested to be good in low-temperature impact resistance and good in appearance. Moreover, good mold release is also requested in order to shorten a molding cycle at the time of injection molding. However, the above-mentioned thermoplastic elastomer compositions were not good in the appearance of tear line parts of air bag covers made thereof to such an extent that painting can be eliminated and also not sufficient regarding mold release.